Previously (yesterday) it was working as 3G, official unlock, no-jailbreak, 4.2.1 (8C148), Firmware 05.15.04.

I then used redsn0w to jailbreak it (yesterday). It worked. I added Cydia and a few addons like SBSettings (today)

Then (today) through the phone I went to Settings > General > Reset > Erase all Content and Settings. As I wanted a 'clean' phone to give to my niece (no data, contacts, history, sms, notes, etc).

During this process, the phone stuck on the black screen with apple.

I tried to jailbreak it again, but this time it got stuck on repatching kernel (I forget the exact phrase). I tried again, no luck.

I tried to restore in iTunes, it downloads 4.2.1 but then says "the iPhone 'iPhone' could not be restored because the firmware file was corrupt." I tried to Shift+Restore and choose the fw file iPhone1,2_4.2.1_8C148_Restore.ipsw manually, but the same thing happens. I have tried with various downloads. Could the fw file really be corrupt, or is there something more serious wrong?

I tried to restore via TinyUmbrella 'start TSS server' and iTunes, still no good. In TinyUmbrella I have iPhone 3G 4.1 (8B117) and iPhone 3G 4.2.1 (8C148) recorded. Trying the former fw in iTunes, it says the firmware is not compatible.

So, my phone is in restore mode, but I can not restore. Or can I? Suggestions please ...

I have also found the same file (same 330,645kbs) on my pc from 18th Jan and that one also has the same problem.

iTunes will 99% extract the file, then fail. I have tried a couple of files and think I used the file successfully back in January so beginning to believe it is a corrupt portion on the phone? I have also had exactly the same result using [iPhone2,1_4.1_8B117_Restore.ipsw], that fails at the last moment of 'Extracting software ..'

I have tried use redsn0w_win_0.9.6b4 with both fw files as well, and it gets to 'replacing kernel' with just a few% done before it gets stuck . It sticks on this screen for 10 minutes before falling back to the apple logo.

I am beginning to think I may have used the wrong redsn0w version (maybe redsn0w_win_0.9.6rc8 or redsn0w_win_0.9.5) by mistake, could that have messed things up?

i have downloaded this one software (iPhone1,2_4.2.1_8C148_Restore.ipsw ) from -http://appldnld.apple.com/iPhone4/06...2_4.2.1_8C148_
wht will be the next step .,.,? is there any need to download any other software to boot or for any other asistancy.,.????
( my i phone is also with a black apple screen)

i have downloaded this one software (iPhone1,2_4.2.1_8C148_Restore.ipsw ) from -http://appldnld.apple.com/iPhone4/06...2_4.2.1_8C148_
wht will be the next step .,.,? is there any need to download any other software to boot or for any other asistancy.,.????
( my i phone is also with a black apple screen)

That firmware only works if you have the same model of iPhone (the 3G). 3Gs or 4 require different files.